222 NEW-YORK FAUNA— MOLLUSCA. 
FAMILY CYCLAD. 
SuEiis covered with an epidermis, and: having on the hinge lateral teeth. Inhabiting pools, 
lakes and freshwater streams. 
Oss. This corresponds with the division Conques fluviatiles of Lamarck. The last named 
species forms a natural transition to this family. It comprises at present four genera, three 
of which are found in the United States. 
GENUS CYCLAS. Lamarck. 
Animal with its mantle with simple edges, and furnished with short and united tubes. Foot 
wide, compressed at its base, and terminated by a sort of appendix. Shell, small, thin, 
oval, inflated, transverse, equivalve. Beaks prominent. Hinge with two very minute 
cardinal teeth; each valve sometimes almost entirely wanting: lateral teeth compressed, 
transversely elongated, lamelliform. Ligament external. 
CycLas SIMILIS. 
PLATE XXV. FIG. 264, 265 (VaR.). 
(STATE COLLECTION.) 
Cyclas similis. Say, Nich. Ency. Ed. Am. p. 4, pl. 1, fiz. 9. 
C. sarratogea et sulcata. Lam. Ane sans vert. Ed. Brux. Vol. 2, p. 388, 
C. similis, GouxLp, Invertebrata of Mass, p. 72, fig. 53. 
Description. Shell suboval, very convex in the adult, nearly equilaterai. Outline varying 
with age; in the young shell, the anterior margin more broadly rounded; in the adult, both 
margins nearly but not quite equally rounded. Basal margin nearly straight. Beaks nearly 
central, slightly elevated and obtuse. Surface with nearly equidistant raised concentric lines, 
giving a sulcate or furrowed appearance to the valves, and generally a more conspicuous ele- 
vated darker wave marking a former stage of growth; these grooves are continued over the 
beaks, which are usually eroded. Hinge with minute very oblique teeth: the lateral ones 
very distinct, elongated, on one side terminating in an elevated triangular point; on the other, 
bifid, with an intermediate longitudinal slit in one valve, and an oval pit in the other. 
Color. Epidermis varying from waxen to reddish brown; within bluish or bluish white. 
Vertical axis, 0°2 — 0°5; transverse ditto, 0:25- 0:6. 
This is found occasionally of somewhat larger dimensions. It occurs in ponds and streams 
in various parts of the State. Under the name of C. solida (fig. 265), I had described and 
figured in my notes a shell, which more mature consideration induces me now to refer to the 
C. similis. It is very solid, subelliptical, convex, with concentric wrinkles; beaks nearly 
